A housing unit is occupied if it was the usual place of residence for the person or group of persons living in it at the time of enumeration. Included are units occupied by persons who were only temporarily absent (for example, on vacation) and units occupied by persons with no usual place of residence elsewhere.

Excerpt from:

Social Explorer; U.S. Census Bureau; U.S. Censuses of Population and Housing: 1960. Census Tracts. Final Report PHC(1)-11. U.S. Government Printing Office, Washington, D.C., 1962.

A housing unit is vacant if no person were living in it at the time of enumeration. However, if its occupants were only temporarily absent, the unit was considered occupied. Units temporarily occupied by persons having a usual place of residence elsewhere were considered vacant (classified as not resident units in 1950).
Year-round vacant units are those intended for occupancy at any time of the year. Seasonal vacant units are those intended for occupancy during only a season of the year.

Available vacant units are those which arc on the market for year-round occupancy, are in either sound or deteriorating condition, and are offered for rent or for sale. The group for sale only is limited to available units for sale only and excludes units for rent or sale. The group for rent consists of units offered for rent and those-offered for rent or sale. The 1960 category available vacant is comparable with the 1950 category vacant nonseasonal not dilapidated, for rent or sale.

Othervacant units comprise the remaining vacant housing units. They include dilapidated units, seasonal units, units rented or sold and awaiting occupancy, units held for occasional use, and units held off the market for other reasons. This category is comparable with the 1950 category other vacant and nonresident.

Excerpt from:

Social Explorer; U.S. Census Bureau; U.S. Censuses of Population and Housing: 1960. Census Tracts. Final Report PHC(1)-11. U.S. Government Printing Office, Washington, D.C., 1962.

Data are presented on condition and plumbing facilities in combination. The categories represent various levels of housing quality.

The enumerator determined the condition of the housing unit by observation, on the basis of specified criteria. Nevertheless, the application of these criteria involved some judgment on the part of the individual enumerator. The training program for enumerators was designed to minimize differences in judgment.

Sound housing is defined as that which has no defects, or only slight defects which are normally corrected during the course of regular maintenance.

Deteriorating housing needs more repair than would be provided in the course of regular maintenance. It has one or more defects of an intermediate nature that must be corrected if the unit is to continue to provide safe and adequate shelter.

Dilapidated housing does not provide safe and adequate shelter. It has one or more critical defects, or has a combination of intermediate defects in sufficient number to require extensive repair or rebuilding, or is of inadequate original construction. Critical defects result from continued neglect or lack of repair or indicate serious damage to the structure.

In 1950, the enumerator classified each unit in one of two categories, not dilapidated or dilapidated, as compared with the three categories of sound, deteriorating, and dilapidated in 1960. Although the definition of dilapidated was the same in 1960 as in 1950, it is possible that the change in the categories introduced an element of difference between the 1960 and 1950 statistics.

The category with all plumbing facilities consists of units which have hot and cold water inside the structure, and flush toilet and bathtub (or shower) inside the structure for the exclusive use of the occupants of the unit. Equipment is for exclusive use when it is used only by the persons in one housing unit, including any lodgers living in the unit.
Units lacking only hot water have all the facilities except hot water. Units lacking other plumbing facilities may or may not have hot water but lack one or more of the other specified facilities. Also included in this category are units whose occupants share toilet or bathing facilities with the occupants of another housing unit. The combination of lacking only hot water and lacking other plumbing facilities is presented as lacking some or all facilities in some census reports.

The categories of plumbing facilities presented in the 1960 report are not entirely comparable with those in the 1950 report. However, the 1950 category no private bath or dilapidated is equivalent to the following 1960 categories: Dilapidated, sound, lacking other plumbing facilities, and deteriorating, lacking other plumbing facilities.